The invention relates to the area of Compact Disc (CD) including all existing or future formats of CD Audio and CD-ROM and any existing or future combinations of compact discs or other optical storage media. In particular the present invention relates to a copy protection and to a copy control mechanism by authentication of optical record carriers, here to a method of obtaining a copy protected optical record carrier, a method of accessing a copy protected optical record carrier and such an optical record carrier itself.
Optical storage discs with information stored on one or both sides have come to be used for a variety of purposes, most notably in the music, games, video and computer industry. Digital information is stored on the optical storage media in the form of pits arranged along circular, concentric tracks on one or on both sides of the disc. The track is typically read from the inside out, but may also be read form outside in, as it is already used for some optical storage media. The data itself on the track is divided into sectors, each equal in length, containing equal amounts of information.
To manufacture an optical storage device, a CD glass master is made by exposing photoresist which is on a glass plate by a modulated laser. The modulation of the laser corresponds to the digital information that is stored on the final disc. Thereafter, exposure, developing and removing those exposed spots form tiny indentations in a single spiral on the glass master are conducted. The pattern and the length of the indentations along this track represent the recorded information digitally. Usually, in a following galvanic process nickel is applied to this glass master to get the nickel master which is the tool for moulding replicas in an injection moulding process. The pattern of the nickel master referred to as pits and land as illustrated in FIGS. 1a and 1b is then embossed on the surface of a polycarbonate or PMMA substrate, which results in a copy of the nickel master that forms the basis of the optical storage disc. The stamped replicas are then coated with a reflective (aluminium or gold) layer and in order to prevent this reflective layer from oxidation a protective layer is applied to the discs.
FIGS. 2a and 2b illustrates the readout of a Compact Disc. A laser beam is focusing onto the surface of the disc. If the laser light falls on the land area most of it will be reflected. If the laser falls on a pit area the light will be refracted and scattered and only a small portion will return in the original direction. This means that the readout electronics can differ between a xe2x80x9c0xe2x80x9d or xe2x80x9cNOxe2x80x9d and a xe2x80x9c1xe2x80x9d or xe2x80x9cYESxe2x80x9d information and furthermore the electronics of a CD reader can reconstruct the digital information which was recorded onto the disc originally.
Although audio reproduction was the primary motivation for development of the CD, and because of cost reductions resulting from the popularity of audio CDs, the CD has recently become a preferred form for storing data for a computer in the form of read only memory, i.e. CD-ROM.
The format in which audio information is stored on a CD is known as the xe2x80x9cRed Bookxe2x80x9d standard. Under Red Book digital data on a CD is organized into indexed tracks. As illustrated in FIG. 4, the digital samples for left and right audio channels are interleaved with error correcting codes, so called C1. C2 error corrections, and SUBCODE data into organized CD blocks. Throughout the disc, the interleaved SUBCODE information defines the current position in minutes, seconds, frames, both with respect to the current track and with respect to the entire disc.
The so called xe2x80x9cYellow Bookxe2x80x9d standard is typically as a format for a CD-ROM. The Yellow Book format is similar to the Red Book format in many respects, including the use of data organized into tracks, interleaved with error correction code and SUBCODE information but replacing the Audio information by computer data. Besides the Red Book and Yellow Book standard there exist many more standards developed for optical storage media covering audio data, computer data, video data and combinations of these information.
According to these standards every block of a CD has to be accessible.
FIG. 3 illustrates a standard CD-ROM mode 1 data sector which consists of 12 bytes MAINCODE SYNCHRONIZATION FIELD, 3 bytes ADDRESS, 1 byte MODE, 2048 byte of USER DATA, 4 bytes ERROR DETECTION CODE, 8 bytes of ZEROS and 276 bytes of ERROR CORRECTION CODE. Such a CD-ROM data sector, i.e. CD block or block, comprises 2352 bytes and is {fraction (1/75)} (one seventy-fifth) of a second.
The 2352 bytes of 1 data sector are carried in 98 Frames depicted in FIG. 4, wherein each Frame includes 24 bytes of said data sector. Additionally to this data, each Frame comprises 4 bytes C2 error correction, 4 bytes C1 error correction and 1 byte SUBCODE data. The 1 byte SUBCODE data is divided into 8 SUBCODE channels called SUBCODE P, Q, R, S, T, U, V. W field, which are also shown in FIG. 4. Each SUBCODE channel consists of 98 bits that are build by 2 synchronization bits and 96 data bits.
As is illustrated in FIG. 5, a SUBCODE Q channel consists of 98 bits, which is referred to as SUBCODE Q field in this invention. All other SUBCODE channels (P, R, S, T, U, V, W) are similar to the Q channel, but carry different information. The first 2 bits of each SUBCODE channel represent the SUBCODE SYNC patterns S0 and S1. These patterns are necessary to synchronize a CD reader to spin the CD at a constant linear velocity.
Each SUBCODE channel has a different function and content, the following description refers to the SUBCODE Q channel only.
The next 4 bits after the SUBCODE SYNC patterns represent the CONTROL FIELD which describes the kind of information of a track as shown in table 1.
The next four bits represent the ADDRESS FIELD and specify the mode. There are several modes (e.g. mode 1, mode 2, mode 3) but for the background of this invention the address mode 1 is explained in detail only.
For mode 1 there are two different data formats possible. For the background of this invention an explanation of the program and lead-out area only of the SUBCODE Q channel is given, as it is illustrated in FIG. 5.
TNO, 8 bits, represents the track number running from 0 to 99. A track numbered with AA represents the lead-out track.
X, 8 bits, represents the index number within a track which can range between 0 to 99.
MIN, SEC, FRAME, 8 bits each, is the running time within a track expressed in 6 digits BCD, The minutes of a track are stored in MIN, the seconds are stored in 10 SEC and the frames are stored in FRAME. One second is subdivided into 75 frames (from 0 to 74).
ZERO, all 8 bits are set to zero (0x00).
AMIN, ASEC, AFRAME, 8 bits each, is the running time on the disc expressed in 6 digits BCD. The minutes of a track are stored in AMIN, the seconds are stored in ASEC and the frames are stored in AFRAME. One second is subdivided into 75 frames (from 0 to 74).
CRC is a 16 bit cyclic redundancy check on CONTROL, ADDRESS, TNO, X, MIN, SEC, FRAME, ZERO, AMIN, ASEC, and AFRAME. On the disc the parity bits are inverted. The remainder has to be checked at zero. The CRC is calculated according to following polynomial:
P(x)=x16 +x12 +x5 +1
The 16 bit CRC field is a parity information that checks the correctness of the CONTROL, ADDRESS, TNO, X, MIN, SEC, FRAME, ZERO, AMIN, ASEC, and AFRAME fields.
Despite apparent advantages of CD-ROM there remain some drawbacks to use a compact disc for marketing and selling large and expensive software packages. A serious drawback is that there is currently no reliable method of protecting a CD-ROM from being copied. The content of a CD-ROM nowadays can be copied onto a hard disc drive or directly onto a CD-Recordable, i.e. CD-R. The software packages illegally copied on a CD-R or on a hard disc drive of a computer will again work without any technical problems.
Therefore, it is an object of the present invention to provide a method of preventing copies of original optical record carriers to be made, in particular a method of creating a key on an original optical record carrier which cannot be copied onto another data carrier and a method of extracting that key off the original optical record carrier in order to be able to distinguish between an original optical record carrier and a copied optical record carrier. Further, it is an object of the present invention to provide an optical record carrier that has a secure copy protection.
The method of obtaining a copy protected optical record carrier carrying information in different blocks according to the invention comprises the following steps:
(a) define number and addresses of blocks used for copy protection;
(b) convert number and addresses selected in step (a) into a copy protection key:
(c) secure information data to be recorded onto the record carrier with copy protection key obtained in step (b);
(d) create a master having modified subcode fields for blocks selected in step (a) and secured information data in other blocks; and
(e) replicate record carrier with master created in step (d).
The method of accessing a copy protected optical record carrier carrying information in different blocks according to the invention comprises the following steps:
(a) find blocks having a modified corresponding subcode field;
(b) extract a copy protection key from a pattern of said blocks having a modified corresponding subcode field found in step (a); and
(c) retrieve data from the record carrier according to the copy protection key extracted in step (b).
The optical record carrier carrying information in different blocks according to the invention is characterized in that individual accessible blocks in a predetermined pattern carry modified subcode information.
Preferred embodiments of the invention are defined in the respective subclaims dependent on the independent claims 1 and 9.
An embodiment of the present invention concerns a method of creating compact discs that carry a unique identifier, which can also be named as key or fingerprint, since this unique identifier is realized by generating blocks that have modified subcode fields in a predetermined pattern. This method is applicable to mass production. In a further embodiment, a method is described of how to retrieve this identifier and a computer equipped with a CD-ROM drive.
Any data can be stored on the optical storage media, the present invention does not require special data to be recorded nor is there any limitation in the amount of the data in regard to this invention.
In a preferred embodiment, the fingerprint or key of the compact disc is incorporated by implementing a certain amount of SUBCODE Q field modifications throughout the program area of the disc. These SUBCODE 9 field modifications result in invalid SUBCODE g fields. On the other hand, a CD block corresponding to an invalid SUBCODE Q field is still accessible, since its address is also stored in the main code header, as it is shown in FIG. 5.
According to another aspect, the present invention is applicable to a method of encrypting at least one part of a main application or data files stored on a compact disc and the decryption of this at least one encrypted part after retrieving the correct fingerprint of the compact disc by using the copy protection key as the decryption tool.
According to a further aspect, the present invention can be used to implement one or more keys on a compact disc in form of various SUBCODE Q field modification patterns.
The main advantage for a user is that no keys have to be entered during the authentication process of the copy protected record carrier, as the predetermined pattern of blocks with modified subcode information is known before the manufacturing and can be implemented in the data included on the respective record carrier. In combination with external keys, that have to be entered during the access procedure, e.g. by the user, for example also only parts of the content of a compact disc can be unlocked from an original disc. This feature allows the possibility of creating multiple language versions or more or less enhanced versions of a software package which can be restored off an original disc only by xe2x80x9cpay for unlockxe2x80x9d.
This invention is not restricted to any specific format of the wide variety of optical storage media, i.e. audio data, computer data, video data or combinations therefrom, it is rather applicable to all existing optical storage media formats.
As will be shown in the following detailed description of the present invention, CD readers return different results when retrieving sectors, i.e. blocks, which correspond to valid or invalid SUBCODE Q fields. Based on those differences the extracted key will be utilized to descramble or decrypt those parts of the main application that have been encrypted before. If the decryption was done with the correct key upon retrieving it from an original disc, or in other words, it the decryption was done with the same key that has been used for encrypting the application beforehand, the main application can be fully restored to its generic layout and will properly work on the computer platform that it was designed for. Since the SUBCODE Q fields are normally not directly copied from one disc to another, as the main code data, but are newly generated during the copy process, retrieving a key from a copied or non original disc will result in a different key than the one that has been used for encrypting, and will furthermore result in a different decryption process and decryption result. Therefore it is not possible to execute such a decrypted application on the computer platform that it was designed for.